PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 721 
Brachial valve with umbo a fairly deep pit and with interarea overhanging 
the exterior slightly. Umbonal pit continued anteriorly for a quarter the length 
of the valve as a shallow depression. Areas flanking this depression slightly 
concave; posterolateral extremities flattened. Geniculated area nonexistent at 
the cardinal extremities but rising medially to form a prominent anterior boundary 
to the concave valve. Interarea fairly long, hypercline. 
Interior of pedicle valve with elongate diductor impressions and strong termi- 
nal callosities. Interior of brachial valve with strong median ridge extending 
anteriorly to the place of geniculation. Adductor field small. Inner marginal 
ridges strong. 
Measurements in mm.—Hypotype (117425a), length 20.3, width 16.7, hinge 
width 21.4+, thickness 5.0. 
Types.—Figured hypotypes: 117425a-c,e. 
Horizon and locality—Effna formation in Virginia: At McNutt Quarry, 12 
miles southwest of Bland, Burkes Garden (15’) Quadrangle; Porterfield Quarry, 
5 miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle. 
Discussion.—In size and general appearance this species suggest T. medius 
Cooper, but sufficient differences in ornamentation and exterior shape can be seen 
to establish their identity. The angle of geniculation of this species is smaller 
than that of T. medius, and the geniculated portion is less convex and the angu- 
larity more distinct. Although the details of the ornamentation of T. medius 
cannot be determined accurately with the material at hand, the species does not 
seem to have the strong concentric elements that are so conspicuous in T. medius. 
Furthermore, the double character of the larger costellae was not detected in the 
other species. 
TITANAMBONITES MEDIUS Cooper, new species 
Plate 178, B, figures 9-21; plate 185, B, figures 11-13 
Shell large for the genus, semielliptical in outline, wider than long. Cardinal 
extremities acute. Shell widest at or just anterior to the hinge. Lateral margins 
nearly straight, sloping medially ; anterior margin broadly rounded. Surface mul- 
ticostellate. Costellae distant, about 13 in the space of 5 mm. at the front margin. 
Costellae and interspaces covered by fine, elevated, concentric fila, about Io in 
the space of I mm., a strong median costella marking both valves. 
Pedicle valve unevenly convex in lateral profile, the umbonal region moder- 
ately convex, the body of the shell gently convex and the geniculated portion 
fairly convex. Angle of geniculation 115° to 120° and geniculation taking place 
about 17 mm. anterior to the beak. Anterior profile broadly convex. Umbonal 
region narrow at the beak, widening anteriorly at median swollen area. Median 
region somewhat swollen. Posterolateral slopes gently concave to the cardinal 
extremities. Anterolateral and anterior slopes steep. A slight fold may be de- 
veloped on the geniculated third. Interarea orthocline to apsacline, fairly long 
and only slightly curved. Pseudodeltidium narrowly elevated. 
Brachial valve concave and fitting closely into opposite valve. Umbonal re- 
gion a moderately deep pit widening anteriorly into a median area that is some- 
